Mystery whale deaths: Is climate change the cause?

Wednesday, 20 July 2016 02:00
Climate Change Series

Photo: Keri-Lee Pashuk

By Katie McConnell

While on a scientific expedition in Golfo de Penas in April 2015, a team of biologists and sailors stumbled upon hundreds of dead sei whales on beaches in Chilean Patagonia. The mysterious circumstances surrounding the whale deaths have been the springboard for collaborative, international multi-disciplinary projects about the whale deaths and more broadly changes in the Patagonian marine environment.

The third largest whales in the world after blue whales and fin whales, sei whales are on the IUCN Red List and considered globally endangered. Little is known about their population size. They feed on large quantities of small crabs and fish by straining them through their baleen. Sei whales are also known to live solitary lives, so when hundreds of sei whales were found deep inside the labyrinth of shallow fjords and canals in the Golfo de Penas, located south of the Taitao Peninsula in the Aysén region, scientists were puzzled.

After the initial discovery and report, Maria Jose Perez from the University of Chile was able to genetically confirm the identification of 15 sampled specimens from the Chilean fisheries service’s (SERNAPESCA) follow-up investigation in May 2015 as sei whales.

Vreni Häussermann, scientific director of Huinay Scientific Field Station, who led the group of scientists that discovered the whales, and Carolina Gutstein of the National Monuments Council in Chile, are conducting an investigation surrounding the mass mortality. Dr. Gutstein and her students completed the initial count of 335 carcasses by adding data from external reports and a June 2015 overflight of the region. From the orientation of the whales on the beaches, Dr. Gutstein concluded that they had not actively beached themselves, and instead had died at sea.

“It was very puzzling,” said Häussermann in an interview. “When looking at current and wind models for the area, developed by our colleagues from Scottish Association of Marine Science, some whales could have died in the open ocean, their supposed habitat, and been washed ashore. However, we cannot really explain how the whales ended up in the shallow and narrow inlets unless they actively swam in.”

The enigma behind the final resting places of the whales remains unsolved, and scientists are still investigating the sei whale’s cause of death. Additional analyses have ruled out other potential causes of death, including those of anthropogenic origin. Except for two small lighthouses managed by the Chilean military, the indigenous village Puerto Eden is the nearest human settlement and situated more than 200 km south of the gulf. Without many clues from the carcasses themselves, which were already quite decomposed when found, scientists continue to look for answers in the greater marine environment of Chilean Patagonia.

Sei whales are on the IUCN Red List and considered globally endangered. Photo: Vreni Häussermann

El Niño
The Patagonian summer of 2014-15 experienced effects of a developing, weak El Niño, based on the Oceanic Niño Index (ONI), the United States’ National Oceanic and Atmospheric Administration (NOAA) standard for identifying El Niño and La Niña events. This small weather event was the precursor to this year’s “Super El Niño,” which may have been the first link in a chain of events that altered the whales’ fate.

In the southeast Pacific Ocean, El Niño events are characterized by a relaxing and sometimes switching of predominant winds, which eases coastal upwelling of nutrient rich water, brings wetter winters with more precipitation, and allows for the intrusion of a large mass of warmer surface water.

This “purple blob” of warmer water, named for its appearance on oceanographic models, tends to hit just the northern and central coasts of Chile, extending about only as far south as Valparaiso. However, this change induces a meteorological shift which pushes high pressure systems further south into Patagonia-- sending more sunny days, less rain (less freshwater runoff) and enhanced conditions for phytoplankton blooms in coastal waters.

Lethal phytoplankton
Phytoplankton are microscopic, unicellular organisms that resemble plants in their capability to conduct photosynthesis. These organisms mostly drift in the water column of the world’s oceans, and are primary producers– meaning that they photosynthesize their energy from the sun. Not only are they the basis and oftentimes drivers of the oceanic food chain, but phytoplankton account for at least 50% of the Earth’s oxygen supply.

But some phytoplankton species may produce biotoxins that can be dangerous to other animals if ingested. Blooms of this kind are known as harmful algae blooms (HABs), or red tide events, even though they may turn the ocean red, green, orange, or a variety of other colors.

One of the most notorious effects of red tide is paralytic shellfish poisoning (PSP), which occurs when the phytoplankton species Alexandrium sp. is eaten by shellfish, such as mussels, and other filter-feeding organisms like small crabs and fish. Red tide biotoxins are thus concentrated in the tissues of these animals, turning them into vectors for the poisons. Although these shellfish and other animals may live unaffected by the Alexandrium or other species of harmful phytoplankton, there are many cases of human and animal deaths from consumption of affected fish and shellfish across the globe.

David Cassis, a phytoplankton expert at the Center for Investigation and Innovation for Climate Change (CIICC) at Santo Tomás University in Santiago, has been closely watching phytoplankton blooms worldwide for the past 20 years. Cassis says that because Alexandrium can take advantage of slightly warmer water temperatures in order to bloom, their increasing prevalence may be an artifact of climate change. “Since 1972, and especially in the last few years, we have seen a sharp increase in the frequency of toxic blooms of Alexandrium catenella throughout the southern fjords,” said Cassis, citing information from HAB monitoring conducted by researchers under Chilean authorities and global watch programs. In addition, studies show that the extra sunlight from the good weather and altered salinities provided by El Niño bring elevated levels of toxic blooms.

Alexandrium catenella. Photo: David CassisTwo species of Ceratium. Photo: David Cassis

But could red tides have killed the whales last summer? The prey sources of the sei whales - sardines and squat lobsters - can also accumulate these biotoxins and thus act as vectors, say scientists.

Local monitoring programs under the Chilean organizations IFOB and CEQUA measure red tide toxins in shellfish once a month throughout Chilean Patagonia in order to close affected fisheries in the event of a toxic outbreak. In March 2015, just before the discovery of the whales, an extremely strong toxicity, nearly ten times the concentration of standard closing limits, was measured at a monitoring site closest to the majority of the dead whales.

If the whales had ingested contaminated prey, then they may have become sick and died.

To test this, the stomach contents of two whales and the tissues of nearby shellfish were tested for biotoxins during a May 2015 SERNAPESCA expedition. Both sources confirmed the presence of red tide. However, since the whales were estimated to have died several months prior, these results were not enough to confirm red tide as their killer.

Still, there are other cases of lethal HABs potentially affecting whales. Last year, nearly 30 other whales—fin, humpback, and grey whales-- were found dead off the coast of continental Alaska. Many researchers speculate HABs are to blame, and NOAA’s monitoring efforts in the area also picked up on more prevalent blooms as a result of El Niño’s effects in the northeast Pacific.

Another clue comes from deep within South America’s past. Gutstein’s analysis of the orientation of the whales on the shores of Golfo de Penas shows similarities to a possible red tide event uncovered from the Miocene era in Cerro Ballena, northern Chile, where the skeletons of about 40 cetaceans lie buried in the dust of the Atacama Desert. Because of the recurrent nature of red tides, Gutstein was not surprised to find the presence of dozens of older skeletons near the new whales in central Patagonia. And, from analyses of the carcasses’ state of decomposition, she estimated that nearly 90% of the 335 whales may have died during one event of about three months.

Some scientists predict climate change may produce more frequent and intense El Niño events, which bring changes in oceanographic conditions with them that seem to be associated with the increases in HABs. Thus, intoxications via HABs may be a critical and as of yet underestimated factor in the conservation of endangered marine mammals.

Scientists are still investigating the sei whale’s cause of death. Photo: Vreni Häussermann

Ocean acidification, a complex threat

As much as climate change is a predominant force throughout Patagonia, its effects are also intertwined with those of overall global change, a term used to refer to planetary-scale changes. Since global change includes all life and physical systems on Earth, worldwide social and industrial change over time may also be influencing oceanic processes in the Patagonian fjords. While the Ocean-Atmosphere Interface-- the part of the sea’s surface that absorbs and recycles carbon-dioxide from the atmosphere-- becomes over-saturated with human-induced CO2, the chemical equilibrium of the water begins to change and its pH begins to drop. This gradual decrease in pH is known as Ocean Acidification.

The drop in seawater pH can turn the seawater corrosive for the mineral that conforms the shells and other structures of many marine organisms (calcium carbonate), so Ocean Acidification is considered especially threatening to calcifying organisms. Scientists are especially concerned that shallow-growing, cold-water coral banks, which are unique to Patagonia, may be at especially high risk.

Dr. Rodrigo Torres, an expert in ocean acidification at the Center for Patagonian Ecosystem Investigation (CIEP) in Coyhaique, has seen that the chemical composition for most of the surface waters of the Patagonian archipelago are almost corrosive for some forms of calcium carbonate. “This is because colder water facilitates CO2 dissolution, and also because precipitation and ice-melt makes inner waters of the Patagonian archipelago fresher, thereby reducing the buffer capacity of surface waters,” he says. In the future, Patagonia may see the beginning of ocean acidification’s corrosive effects.

Most interesting for the whales’ story, however, may be how ocean acidification affects the toxicity of some organisms. Recent research published in 2012 from A. Tatters and colleagues showed how high levels of CO2 can even promote the production of PSP by Alexandrium cantenella. With climate change seeming to provide better conditions for HABs via warming trends and changes in oceanographic conditions during El Niño events, it may be that ocean acidification comes as a double-whammy to marine life by making existing toxic blooms more potent.

A new twist: orca assailants?
Since the first report of the sei whales’ death was made by the Huinay team last year, Chilean authorities and groups of scientists organized by Häussermann and Gutstein have completed four more expeditions to look for more clues.

In early 2016, a multi-disciplinary team spent nearly five weeks in northern Golfo de Penas searching for evidence of red tide, gathering oceanographic data, and making detailed forensic reports for each whale encountered.

Death of sei whales at Golfo de Penas. Photo: Vreni Häussermann

One afternoon, scientists were suddenly caught by surprise when a large pod of orcas chased a sei whale into the shallow fjord where they were working. In one dramatic moment, the sei whale beached itself next to where the scientists stood in order to escape its attackers. Quickly, the sei whale reentered the water and was chased out of sight by the orcas.

Although it is unclear whether the sei whale escaped the orcas or was caught, researchers were saddened to find a newly deceased sei whale on a nearby beach the following morning. Although in the past this behavior has been observed farther south in Tierra del Fuego, witnessing this event has piqued scientists’ curiosity for more information into the presence of orcas in the central Patagonian zone, and has catalyzed the incorporation of natural event sightings and local reports into their research.

However surprising this behavior may be, one observation of orca attacks cannot explain the deaths of hundred of whales nor negate the other components of the investigation. Looking forward, scientists are maintaining a broad approach in their next steps.

The way ahead

As the mystery of the sei whales continues to unfold, its story becomes ever more intricate. Like many scientific journeys, the pursuit of one answer only leads to more questions.

Much of the information garnered by these expeditions are the first of their kind, as the remoteness and extreme weather of the Gulf has hindered the progress of previous scientific endeavors. Since high concentrations of biotoxin blooms were measured in channels south of the Golfo de Penas in March 2016, scientists are anxiously waiting to see how many new victims their next expedition might reveal. “Of course we hope that there will be no new casualties,” mentioned Dr. Häussermann, “be we won’t be sure until we get there.”

In a rapidly changing world where much weight is given to well-known environmental occurrences, perhaps the whales of Golfo de Penas are a call to remember the corners of the globe that have been left overlooked by the passage of time and hidden by the rawness of the Patagonian wild.

The author, Katie McConell, is a marine biologist who has dived extensively throughout Patagonia as a field technician for Fundación Huinay on their scientific expeditions. This article was supported by an EcoPatagonia reporting grant from Patagon Journal in partnership with Earth Journalism Network. More info at www.ecopatagonia.org

Expedition leaders would like to also acknowledge support of Keri and Greg of the sailing vessel Saoirse, Blue Marine Foundation, Fondecyt, National Geographic, NAVIMAG, and PEW.

The results of these expeditions are being compiled into an inter-disciplinary scientific paper: "Largest baleen whale mass mortality during strong El Niño event is likely related to harmful toxic algal bloom." PeerJ.